In my case .h5 files are created by a package created on Trixi.jl with some extension.
Actually I got the solution. Initially, I installed Trixi2Vtk.jl package in --project=. environment then it was showing the key capacity not found error but if I installed Trixi2Vtk.jl in my base i.e. without using flag --project=. then it worked fine and generated the required .vtu files.
Thanks!